Quote Originally Posted by PJG1173 View Post
from what I've read the flow rate shouldn't change much. with the vac ref FP since at idle manifold vac helps draw fuel out of the injectors so less pressure is needed to provide the same amount of flow as higer pressure with lower vac (higher Kpa) signals.
Quote Originally Posted by EagleMark View Post
But don't think theres any coding in MPFI ECM for this as it's handled by the regulater. The vacuum referenced FPR is lower at idle and high vacuum as vauum sucks fuel out, then when vacuum is not present or low like WOT it adds pressure to compensate. Keeping same deleivery of fuel across board.
correct and correct. i actually forgot about the returnless style duel systems that use a FPR that isn't vacuum referenced. i know some LSx cars are like that and for applications i'm used to, the 3500 and 3900 V6 units are actually similar, they have an in-tank pump/regulator combo with no vacuum reference. pretty sure that they don't use a PWM fuel pump either....

and it's pretty easy to allow the ECM to know that you're removing the vacuum reference to lower fuel pressure, just modify the VE table at the various MAP points.